1. Field of the invention
The present invention relates to a light pulse generator apparatus and more particular to a light pulse generator apparatus capable of generating a high power light pulse with a varying width.
2. Description of the prior art
A structure of a light pulse generating apparatus is proposed by the applicant in copending U.S. patent application Ser. No. 910,198 filed on Jul. 8, 1992, claiming the priority of Japanese Patent Application No. 3-197337 filed on Jul. 12, 1991, which is shown in FIG. 2 of this application. In this figure, a reference numeral 1 denotes an optical fiber, 2 denotes a light source for optical pumping, 3 denotes an optical coupler, 7 denotes an optical isolator, 5 denotes an optical switch, 6 denotes an optical switch controller, and 4 is an optical decoupler. The optical fiber is doped with a rare earth element and is optically pumped with the optical pumping light source 2. The output of the light source is supplied to the input terminal 3A of the coupler 3 to lead the output of the light source 2 to the optical fiber 1 by way of the optical isolator 7. The output of the optical fiber 1 is inputted to the optical switch 5. The optical switch controller 6 makes the optical switch 5 close to pass the light to the optical decoupler 4. An optical loop is formed in the apparatus shown in FIG. 2 by the optical coupler 3, the optical isolator 7, the optical fiber 1, the optical switch 5, the optical decoupler 6 and its output terminal 4A connected to the input terminal 3B of the optical coupler 3. A high power light pulse is generated in this loop by closing the optical switch 5 for a short period of time, and the light pulse is withdrawn from the output terminal 4B of the optical decoupler.
3. Problem to be solved
With this prior apparatus, the width of the light pulse can be changed by controlling the length of the time period of the closure of the optical switch 5. However, with the increase in the time of closure of the optical switch a limit is reached where the pulse width is no longer broadened. In order to broaden the pulse width the optical fiber 1 must be replaced with another one doped with a rare earth element having different property and length.
Accordingly, an object of the present invention is to provide a high power light pulse generator capable of changing the light pulse width without replacing the rare earth element-doped optical fiber.